With large rolling bearings for special applications, considerable bending moments and tilting forces sometimes act on the bearing rings which can lead to twisting and to an angular offset of the ball races with respect to one another such that premature wear occurs in the region of the ball races and of the roller bodies. Such large rolling bearings can have dimensions of a plurality of meters in diameter and can, for example, be used on cranes in order, for example, to rotatably support and to prop up the support mast of a ship crane or of a harbor crane, with here not only vertical forces having to be absorbed, but also bending moments or tilt loads. The twisting and tilting problems are in this respect further aggravated when the middle or center of the bearing has to be kept free to allow the component to be supported, for example the named crane support mast, to pass through the bearing or to be able to attach a rotary drive to the part which has to be passed through. The bearing rings of such a center-free large rolling bearing can in particular not be of any desired size in construction, in particular in the radial direction, for space reasons so that the achievable moments of inertia of an area of the ball races are limited.
A large rolling bearing of the initially named kind is shown, for example, in the document EP 2 092 204 B1, in accordance with which the scraper ring of the one ball race is to be clamped by two oppositely disposed axial bearings and two oppositely disposed radial bearings in the groove of the other ball race, wherein the named oppositely disposed axial bearings and radial bearings should prevent unwanted deformation of the scraper ring and should avoid a separation of the ball races in the radial direction. A similar large rolling bearing and its installation situation at the support mast of a ship crane is shown in the document WO 2008/088 213 A2. Whereas the named documents essentially deal with the problems of the separation of the radial bearings as a consequence of twisting of the ball races and endeavor to avoid a lifting of the radial bearings by the clamping of the scraper ring by oppositely disposed jacket surface sides, canting and twisting still occur in the region of the axial bearings.
The vertical crane loads and the corresponding reaction forces in the crane mast support typically still make up a large or considerable part of the rolling bearing load so that the lower axial bearing, which has to absorb the vertical crane loads, is typically configured in the form of a load-carrying cylinder rolling bearing whose cylinder rollers have a relatively large cylinder roller width to have a sufficiently large contact line and to keep surface pressures tolerable. On the other hand, such wide cylinder rolling bearings react critically to tilting or to inclinations of the raceways with respect to one another since here very quickly only a very small proportion of the cylinder rollers is actually bearing.
It is the underlying object of the present invention to provide an improved rolling bearing of the initially named kind which avoids disadvantages of the prior art and further develops it in an advantageous manner. A center-free large rolling bearing should in particular be provided which can absorb high axial loads without in so doing being susceptible to tilt loads and to inclinations of the raceways.
The named object is achieved in accordance with the invention by a rolling bearing having two concentric ball races, wherein a first ball race comprises a groove open toward a second ball race and the second ball race comprises a scraper ring engaging into the groove, wherein the scraper ring is supported at the groove in an axial direction of the rolling bearing by a first and a second axial bearing which are arranged at oppositely disposed front sides of the scraper ring and is supported in a radial direction of the rolling bearing by at least one radial bearing, wherein the scraper ring is supported at the groove in the axial direction by a third axial bearing, with the first and second axial bearings arranged at the front side of the scraper ring in raceways offset from one another in the axial direction.
It is therefore proposed to support the scraper ring with respect to the groove and thus to support the one ball race with respect to the other ball race by a third axial bearing in order also be able to absorb high axial forces with bearings of a narrower construction size and to be able to distribute them over different support points. In this respect, the two axial bearings arranged at the same scraper ring first front side are not only transversely spaced apart from one another, but are also offset from one another in the axial direction in order to achieve different twisting and inclinations and thus greater robustness with respect to twisting and inclinations. In accordance with the invention, the scraper ring is supported in the axial direction at the groove by a third axial bearing, wherein two axial bearings are arranged at the same first side of the scraper ring at separate raceways offset from one another in the axial direction of the rolling bearing. The axial bearings are given different lever support relationships by the axial offset of the raceways of the two axial bearings arranged at the same first side of front side of the scraper ring, even though said axial bearings are arranged at the same first scraper ring side, so that a better support can be achieved in the event of twisting and raceway inclinations and both axial bearings are never simultaneously subjected to canting or lifting in the same way.
The two axial bearings arranged at the same first scraper ring front side can advantageously each have a width which is smaller than the width of the axial bearing arranged at the front side of the oppositely disposed scraper ring. If cylinder rolling bearings are used as axial bearings, the named width is the length of the cylindrical roller bodies and/or the width of the raceway of the bearing. An adaptation of the inclination from a deformation of the connection design is more easily possible by the use of two independent, relatively narrow raceways for the two axial bearings arranged at the first front side of the scraper ring. In addition, two such recessed, relatively narrow raceways in total provide a longer linear contact between the roller bodies and the raceways, in particular even when slight inclinations of the raceways occur due to deformations. In addition, narrow raceways also have to be produced with higher precision from a technical production aspect so that shape tolerances also occur less and have less importance.
The named axial offset of the two axial bearings arranged at the same first front surface side can generally have a different magnitude or dimension. In order, on the one hand, to achieve a noticeable decoupling with respect to twisting and different support relationships, the offset amounts, in a further development of the invention, to at least 10% of the roller body diameter of the two named axial bearings. In order, on the other hand, to achieve a compact bearing geometry and scraper contour overall which does not thin out the scraper ring too much and keeps it stable, the named offset can amount to less than 200% of the named roller body diameter. If the two axial bearings arranged at the first front side of the scraper ring have different roller body diameters, the named offset dimensions advantageously relate to the larger roller body diameter.
The named axial offset of the two axial bearings arranged at the same first front side of the scraper ring can advantageously amount to between 10% and 100%, preferably to approximately 15% to 35%, of the roller body diameter. The offset can in particular be selected such that, viewed in the radial direction, the two rolling bearings still cover one another with their roller bodies.
If the axial bearings arranged oppositely disposed on a first front side of the scraper ring are looked at, the three axial bearings can advantageously have different raceway diameters, with, in an advantageous further development of the invention, at least one of the two axial bearings arranged at the same front side of the scraper ring not having any coverage with the axial bearing arranged at the other front side of the scraper ring when looking at the axial bearings in the axial direction. The named axial direction in this respect means the axis of rotation of the rolling bearing.
In an advantageous further development of the invention, provision can in this respect be made that one of the two axial bearings arranged at the same front side of the scraper ring covers the axial bearing arranged at the other front side of the scraper ring, viewed in the axial direction, whereas the other of the two axial bearings disposed at the same first front side of the scraper ring does not have any coverage with the named axial bearing disposed at the other front side of the scraper ring.
In an alternative further development of the invention, the arrangement of the three axial bearings can also be made such that both of the axial bearings disposed at the same first front side of the scraper ring have no coverage—viewed in the axial direction—with the axial bearing disposed at the other front side of the scraper ring, with provision in particular being able to be made that the axial bearing disposed at the named other front side of the scraper ring is arranged between the two axial bearings disposed at the same front side of the scraper ring, i.e. the roller bodies of the axial bearing disposed at the one front side of the scraper ring run on a raceway diameter which lies between the raceway diameter of the two other axial bearings disposed at a common front side of the scraper ring.
In the radial direction, the scraper ring is advantageously likewise supported at oppositely disposed sides of the scraper ring, with, in an advantageous further development of the invention, two radial bearings being able to be provided which can be arranged at oppositely disposed jacket surface sides of the named scraper ring.
The two radial bearings can in this respect be arranged, viewed in the axial direction, between the axial bearings arranged at oppositely disposed front sides of the scraper ring.
The arrangement of the radial bearings with respect to one another can generally differ in this respect. In an advantageous further development of the invention, the two radial bearings can cover one another, viewed in the radial direction, for example can be arranged in a common plane which is perpendicular to the axis of rotation.
The configuration of the named radial bearings can in this respect be different. In accordance with an advantageous embodiment of the invention, the two radial bearing can have roller bodies of different geometries, with one of the radial bearings in particular being able to be configured as a cylinder rolling bearing and the other radial bearing being able to be configured as a ball bearing. On the one hand, high radial forces can be transmitted with a compact radial construction due to the use of the cylinder rolling bearing, whereas, on the other hand, forces with axial components can also be carried off by the ball bearing which also has a support effect in directions inclined with respect to the radial direction.
In an alternative further development of the invention, however, both radial bearings can also have the same roller body type or the same geometrical type and can in particular both be configured as cylinder rolling bearings.
The invention will be explained in more detail in the following with respect to preferred embodiments and to associated Figures.